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Ever wonder why a "Halogen" light bulb has that name? Well, what happens if you try to create a very bright incandescent lamp is that when pumping so much electricity through a filament and heating it up to incredible temperatures you'll actually start to evaporate the filament. This is a common failure mode for incandescent bulbs, a part of the filament will get thinner due to evaporation and then the reduced thickness will increase resistance in that section, accelerating evaporation and eventually causing a break. But if you put a small amount of Bromine or Iodine gas (halogens) inside of the bulb, and a small amount of Oxygen, then the evaporated metal will form a Tungsten OxyHalide gas which will then redeposit Tungsten metal through an electro-chemical reaction back onto the filament, increasing the filament's longevity even at very high power levels.

> A regular light bulb converts about 2% of its energy input into light, and 98% into heat.

This isn't relevant to your argument, but that actually isn't true, that figure is about 6~8 percent.

* The "luminous efficiency" as commonly reported is just the lumen/W luminous efficacy divided by the peak value of 683lm/W. The value of 683lm/W is the peak of human eye sensitivity curve and occurs at 555nm. The only light source that can achieve 100% "efficiency" by that measure is a 100%-efficient radiator that emits monochromatic 555nm (bright green) light, the best a perfect white light source can do is about 37%. (see [1])

* That "perfect white light source" would be a 100%-efficient radiator emulating the Sun spectrum bandlimited to visible light (zero infrared, uv and no other losses).

* It's possible to make a light source that appears white to human eye and is more efficient than that by emitting mostly at wavelengths the human eye is more sensitive to, and emitting less at wavelengths it's less sensitive to. That's part of the reason why manufacturers often offer CFLs with high efficiency but poor color rendering and lower efficiency but higher color rendering. (And don't get me started on the color rendering index.)

* That definition of "efficiency" is obviously not what most people think it is when they hear that word (useful work / total work spent), some prefer to call it "luminous coefficient". But it's not all lies, it was defined that way because it's easy to compute and understand and because this is the value of interest if e.g. you're making a LCD backlight or if you're designing an interior lighting setup.

[1]: https://en.wikipedia.org/wiki/Luminous_efficacy

i'm not comparing LEDs with incadescent bulbs, i'm comparing them with the coiled tubes - cfls. these things - http://en.wikipedia.org/wiki/Compact_fluorescent_lamp

[i thought that was obvious - are you trolling?]

I was just trying to explain how even an "efficient" lamp can overheat. Sorry I overlooked the CFL.

In terms of energy efficiency, CFLs are halfway between incandescent bulbs and LEDs. So the same comparison holds, only the differences are less extreme.

60W-equivalent CFLs use 13-15W of energy. That's approx. 1.25W into light (because the amount of light is more or less the same in all cases) and the remainder (11.75-13.75W) into heat. That's why CFL lamps get rather warm after a while. Very bright CFLs often have slots in the base for ventilation [1].

You just don't notice it as much because:

1) The heat source of CFLs is much larger than LEDs, so the average temperature is lower even though the total amount of heat is higher.

2) With all those coils and folds, CFLs have a larger surface area than most other types of lamps, so they cool easily.

[1] https://en.wikipedia.org/wiki/File:Compact_fluorescent_light...

> In terms of energy efficiency, CFLs are halfway between incandescent bulbs and LEDs.

That isn't true. LEDs are equivalent to CFLs in energy efficiency. The only LEDs that are more efficient are either lying to you (they claim the light is more directed so it "counts" as more, and they uprate the bulb), or they have worse color accuracy so you are not comparing equivalent bulbs.

> The heat source of CFLs is much larger than LEDs, so the average temperature is lower even though the total amount of heat is higher.

No. The heat source is not larger - it's in a different location, it's in the bulb part and it emits infrared light and is sent into the room. With LEDs the heat is made in the base and stays there.

> With all those coils and folds, CFLs have a larger surface area than most other types of lamps, so they cool easily.

That doesn't explain why an incandescent that makes 6 times as much heat can manage, but an LED can't. It's not the cooling of the bulb, it's the type of heat - incandescents and CFLs make their heat in the form of infrared light that is sent into the room.

> The only LEDs that are more efficient are either lying to you (they claim the light is more directed so it "counts" as more, and they uprate the bulb), or they have worse color accuracy so you are not comparing equivalent bulbs.

Let's exclude lying vendors.

Worse color accuracy is annoying for those who care, but as far as total energy output is concerned, it shouldn't matter. A watt is a watt no matter what frequency it is radiated at.

> The heat source is not larger - it's in a different location, it's in the bulb part

Sure. And the bulb of a typical CFL is hundreds of times larger than the die of an LED.

> That doesn't explain why an incandescent that makes 6 times as much heat can manage, but an LED can't.

As I mentioned in the great-great-grandparent comment, glass tubes (CFLs) and tungsten wires (incandescent lamps) are much less sensitive to heat than tiny pieces of delicate electronics are. 85'C is child's play to glass and tungsten but deathly to silicon.

> incandescents and CFLs make their heat in the form of infrared light that is sent into the room.

The "sent into the room" part is definitely correct. LEDs overheat more easily because the heat is generated and trapped in the base. But even if you dangled a bare LED in mid-air, I doubt you could make it as cool as a CFL because the heat source is concentrated in such a small area. I'd also be surprised if those LEDs didn't generate a lot of infrared ratiation.

> but as far as total energy output is concerned, it shouldn't matter. A watt is a watt no matter what frequency it is radiated at.

Ah, but if you are willing to have poor color accuracy then CFLs should be allowed that as well, and if you do that then their energy efficiency is better than an LED.

> glass tubes (CFLs) and tungsten wires (incandescent lamps) are much less sensitive to heat than tiny pieces of delicate electronics are

CFLs have switching power supplies in the base that don't like heat either. It's not just a glass tube. But I'm willing to accept that they can handle heat better than an LED emitter. (And I'm pretty sure it's just the emitter with the problem - it's certainly possible to make "delicate electronics" that can handle heat.)

A watt is a watt no matter what frequency it is radiated at.

the whole discussion above is concerned with the relative amounts radiated in visible and infra-red....

To give you an actual answer to your question:

LEDs and CFLs are about equally efficient, but CFLs produce their heat on the bulb, and LEDs produce their heat in the base.

So CFLs (and incandescents) send their heat out into the room, which cools the bulb. LEDs keep all the heat inside which is a huge problem for them.

Personally I think bulb replacement LEDs are a dead end, and instead you should look for dedicated LEDs fixtures.